Peyer patches

Peyer patches are mucosa-associated lymphoid tissue (MALT) structures found predominantly in the terminal ileum, though they can occur throughout the small intestine. These oval-shaped lymphoid aggregates consist of B cell follicles with germinal centers, surrounded by T cell zones and topped by a follicle-associated epithelium (FAE). The FAE contains specialized microfold (M) cells that lack microvilli and actively transport antigens from the intestinal lumen to underlying antigen-presenting cells. This antigen sampling initiates both protective immune responses against pathogens and tolerogenic responses to commensal bacteria and dietary antigens. Peyer patches are most numerous during childhood and adolescence, then gradually decrease with age. They serve as inductive sites for IgA production, which is secreted into the intestinal lumen for mucosal protection. Clinically, Peyer patches can become inflamed in conditions like typhoid fever (rose spots may correlate with Peyer patch inflammation) and can be sites of lymphoma development, particularly in immunocompromised patients. They also play a role in inflammatory bowel diseases and food allergies through dysregulated immune responses.